Etching process includes dry etching and wet etching. The dry etching may bring plasma damages to the sensitive devices on the silicon wafer. Currently, the wet etching plays an important role in the semiconductor manufacturing field. The anisotropic wet etching of silicon has been very popular in the wet etching. The anisotropic etchant is generally divided into organic etchant and inorganic etchant. The organic etchant includes EPW (ethylenediamine, pyrocatechol and water), hydrazine, TMAH, and so on; the inorganic etchant includes alkaline etching solution such as KOH, NaOH, NH4OH, and so on. During the process of the anisotropic wet etching of silicon, the different crystal orientations of the silicon have different etching rates, i.e. the etching rate is closely related to the crystal orientation of the silicon. In addition, the anisotropic etching rate of silicon is also related to the type and ratio of the etchant, the reaction temperature and other parameters. Therefore, the fluctuation of the etching rate may be great, that is difficult to control the etching depth. In the semiconductor device, the slight difference of the size of the device affects the device performance. Therefore, it is important to use effective means to monitor the silicon wet etching depth.
Currently, there are several ways to monitor the silicon wet etching depth. First, a microscope with a depth (Z axis) measuring is used to measure the depth; second, 3D profilometer or scanner is used to measure the depth. In which, the first way has a relatively low accuracy, the error is usually beyond 10 μm; especially, the accuracy is much lower when the etching depth is very deep (such as several hundred microns). Moreover, the microscope with the depth (Z axis) measuring is very expensive. It has a high accuracy of the second way, but dedicated measurement equipments are needed, such dedicated equipments are usually quite expensive. Moreover, in both of the above measurement ways, the etching sheet is needed to remove for several times during the etching process, and then the etching area is measured, thus the etching depth is monitored. Plenty of time and manpower are cost for every measurement step; the production efficiency is seriously affected.
Accordingly, it is necessary to provide a monitoring method with low-cost, which can control the silicon wet etching depth.